1. Technical Field
This invention is directed to thermosetting polymers and particularly to a polybutadiene capable of exhibiting heat resistance at a ultrahigh level. The invention relates further to a process for the production of such polymers.
2. Prior Art
A variety of synthetic polymers have recently found usage as engineering plastic materials which enjoy credit in certain sectors of industry as good substitutes for structural materials such as metals and metal oxides. Weight saving, corrosion resistance and electrical insulation are the primary characteristics peculiar to the synthetic polymers. Engineering plastic materials, in addition to those qualities, are required to be thermally resistant and mechanically strong. Heat resistance in particular can be regarded as determinant of and critical to the nature of such engineering plastics.
Prior polymers of an engineering plastic grade include a thermosetting class of epoxy resin, unsaturated polyester resin, phenol resin, polybutadiene resulting from curing by radical initiation and the like and a thermoplastic class of nylon-66, polycarbonate, polyphenylene oxide, polyethylene terephthalate and the like. Further, polyphenylene sulfide, polyimide, wholly aromatic polyester and the like are in common use as a special class.
The foregoing plastic materials, however, are totally unsatisfactory as they are in most cases prone to encounter too low a heat distortion temperature (HDT). This temperature is taken as a measure of heat resistance and desired to be above 250.degree. C. for those plastic materials from a commercial point of view. Although sufficient in terms of exceeding 250.degree. C. in HDT, a certain limiting class of polymers are disadvantageous in that they require elevated temperature on melting, say 350.degree. C. and even higher, and hence result in reduced moldability. One such example is a wholly aromatic polyester of a liquid crystal type.
Butadiene polymers can cure-reacted, as is commonly accepted in the art, usually at a temperature of 100.degree. to 160.degree. C. and typically with the use of an organic initiator such as dicumyl peroxide. This prior mode of curing fails to sufficiently crosslink the polymer at its vinyl groups and thus leads to a small reactivity in the range of 5 to 15%, eventually producing a cured molding with too low an HDT temperature of about 60.degree. to 110.degree. C.
Thus the existing situation of the prior art has lent an impetus for the provision of butadiene polymers which enable pouring into molds at a lower temperature than 200.degree. C. and on curing have a higher HDT temperature than 250.degree. C.